Well, the numbers I find on google are: a Nvidia 4090 can transfer 1008 GB/s. And a i9 does something like 90 GB/s. So you’d expect the CPU to be roughly 11 times slower than that GPU at fetching an enormous amount of numbers from memory.
I think if you double the amount of DDR channels for your CPU, and if that also meant your transfer rate would double to 180 GB/s, you’d just be roughly 6 times slower than the 4090. I’m not sure if it works exactly like that. But I’d guess so. And there doesn’t seem to be a recent i9 with quad channel. So you’re stuck with a small fraction of the speed of a GPU if you’re set on an i9. That’s why I mentioned AMD Epyc or Apple processors. Those have a way higher memory throughput.
And a larger model also means more numbers to transfer. So if you now also use your larger memory to use a 70B parameter model instead of an 12B parameter model (or whatever fits on a GPU), your tokens will now come in at a 65th of the speed in the end. Or phrased differently: you don’t wait 6 seconds, but 6 and a half minutes.
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So if I had more memory channels it would be better to have say ollama use the cpu versus the gpu?
Well, the numbers I find on google are: a Nvidia 4090 can transfer 1008 GB/s. And a i9 does something like 90 GB/s. So you’d expect the CPU to be roughly 11 times slower than that GPU at fetching an enormous amount of numbers from memory.
I think if you double the amount of DDR channels for your CPU, and if that also meant your transfer rate would double to 180 GB/s, you’d just be roughly 6 times slower than the 4090. I’m not sure if it works exactly like that. But I’d guess so. And there doesn’t seem to be a recent i9 with quad channel. So you’re stuck with a small fraction of the speed of a GPU if you’re set on an i9. That’s why I mentioned AMD Epyc or Apple processors. Those have a way higher memory throughput.
And a larger model also means more numbers to transfer. So if you now also use your larger memory to use a 70B parameter model instead of an 12B parameter model (or whatever fits on a GPU), your tokens will now come in at a 65th of the speed in the end. Or phrased differently: you don’t wait 6 seconds, but 6 and a half minutes.